It is common for audio or video data to be transformed from one domain to another in order to facilitate desired signal processing. For example, pulse code modulated (PCM) audio data generated by a transducer such as a microphone may be transformed from a time domain to a frequency domain, in order for it to be compressed.
Typically, transformation of audio or video data from one domain to another is done using a transform selected due to its suitability for the type of signal processing at hand. For example, if it is compression that is to be performed on audio or video data, the modified discrete cosine transform (MDCT) may be used to transform the audio or video data into a frequency domain; the MDCT's suitability for compression is well known.
It is not uncommon for audio or video data to sequentially undergo two or more different types of signal processing. For example, PCM audio data generated by a transducer such as a microphone may be processed to reduce noise (first signal processing) before being compressed (second signal processing). Typically, the different types of signal processing would involve respective different transforms.